The power requirements of a core memory are directly related to the number of zeros to be written into or read out of the core memory. That is, there is an increased power consumption in the memory core where the content of a data word contains more zeros than ones. A substantial power saving can be effected by means capable of determining when it would be advantageous to reverse the polarity of the input data word when writing into the memory. Of course, each word in the memory must contain an additional bit to indicate if the polarity of that word has been reversed so that it can be restored to its original polarity when read out.
In the past, devices using this method of conserving power have employed analog rather than digital techniques. The analog method involves converting the data input from digital form to a voltage level whose magnitude is compared to a reference voltage. The disadvantages of the analog method are that it requires numerous expensive parts and it is not readily expanded as the size of the data word increases.